The fusion of mouse myeloma cells to spleen cells from immunized mice by Kohler and Milstein in 1975 [Nature 256, 495-497 (1975)] demonstrated for the first time that it was possible to obtain continuous cell lines making homogeneous (so-called "monoclonal") antibodies. Since this seminal work, the need has existed for methods for the purification of monoclonal antibodies. Various cell surface proteins expressed by different strains of bacteria have been employed for this purpose. For example, Protein A, a protein isolated from Staphylococcus aureus which binds to the Fc region of immunoglobulins, and Protein G, an immunoglobulin binding, bacterial cell wall protein isolated from group G streptococcus bacteria, have been employed in the purification of both monoclonal and polyclonal antibodies. Protein G has been shown to bind to various animal and human antibodies, including bovine, chicken, goat, mouse, rabbit and rat polyclonal IgG, some mouse monoclonal antibodies, and human IgG1, IgG2, IgG3 and IgG4, in addition to albumin from various sources.
Despite this knowledge, there is a need for improved methods for the purification of monoclonal antibodies utilizing Protein G.